As society becomes increasingly mobile, there is an ever-growing demand for electronic devices that are more powerful and more portable. In general, technology has answered this demand with lighter and stronger materials, and miniaturized electronics. For example, modern cellular telephones are small enough to be carried in a shirt pocket and powerful enough to send and receive electronic mail.
One drawback, however, of creating smaller devices is the decreasing amount of surface area on which to locate a convenient user interface. From an ergonomic point of view, the smaller the human interface is on a portable device, the harder it is to operate. Moreover, as a portable device becomes more capable, a more complex interface for the device is typically needed. Thus, there is increasing difficulty in portable device design to achieve devices that are smaller and more powerful, yet convenient to use.